1. Field of the Invention
The present invention relates to an active matrix type of liquid crystal display apparatus and its driving method. In particularly, the present invention relates to a driving technique to improve quality of moving picture image.
2. Description of the Related art
FIG. 8 is a perspective figure showing a configuration of the active matrix type liquid crystal display apparatus of the related art. As shown in FIG. 8, the display apparatus of the related art has a panel structure comprising a pair of insulator substrates 101, 102 and liquid crystal 103 held in between those two substrates. A pixel array unit 104 and a drive circuit unit are fabricated and integrated on the insulator substrate 101 disposed at the lower side. The drive circuit unit consists of a line drive circuit 105 and a column drive circuit 106. A terminal unit 107 for an external connection is fabricated on an upper part of peripheral area of the insulator substrate 101. The terminal unit 107 is connected to the line drive circuit 105 and the column drive circuit 106 via wiring 108. Gate wiring 109 in a line form and signal wiring 110 in a column form are fabricated in the pixel array unit 104. A pixel electrode 111 and a thin film transistor (TFT) 112 for driving the pixel electrode 111 are fabricated at an intersection of the gate wiring 109 and the signal wiring 110. A gate electrode of the thin film transistor 112 is connected to a corresponding gate wiring 109, a drain region to a corresponding pixel electrode 111, and a source region to a corresponding signal wiring 110. The gate wiring 109 is connected to the line drive circuit 105, and the signal wiring 110 is connected to the column drive circuit 106.
Due to technical advancement on devices, process and fabrication, the active matrix type liquid crystal display (LCD) apparatus with a size up to a twenty inch class may be realized now. And brighter and fine picture quality is being developed. Furthermore, improvements are also made on problems relating to narrow viewing angle of the liquid crystal display (LCD), which is considered as one of drawbacks in the LCD, by implementing technologies such as switching of liquid crystal molecules with an electric field along a substrate plane direction (so called in-plane switching), combining of a liquid crystal alignment direction division and a vertical alignment (so called multiple vertical alignment), or using of a phase shift correction film. The problems related to the viewing angle are such that the viewing angle of the LCD in which more than a reasonable contrast can be obtained is narrower than that of CRT, and an negative-positive inversion may be occurred locally for a gray scale image display. Furthermore, according to advancements of production technologies, it enables to cut cost of the LCD considerably and even a twenty inch class LCD television is coming into practical use. With these technologies mentioned above, a picture quality of the LCD has becomes comparable and superior to that of the CRT as far as a still picture image concern.
However, some drawbacks of the LCD are left to be solved. One is an image quality of moving picture. That is the LCD may not be able to generate clear outlines of moving pictures and the moving pictures displayed on the LCD screen may be smear. For example, for an extreme case, a trailing tail image of pitched ball may be appear on the LCD screen during a baseball game broadcasting. Such an extreme case is now being resolved due to an technical advancement on liquid crystal material. Quantitatively, a total period (i.e. response time) of a rise time for horizontally oriented liquid crystal molecules to be risen with an certain electric field and a fall time for the risen liquid crystal molecule to go back to the original orientation with null electric field is reduced to as short as about 30 msec due to technical improvement. Presently, liquid crystal molecules are driven to rise or fall at the beginning of every 33.3 msec frame period for the LCD with a 30 Hz frame frequency. In other words, the response characteristic of the LCD has been improved so much as that the liquid crystal molecules can be driven to follow the frame frequency without any difficulties.
However, the problem on clarity of the moving picture outlines remains unsolved. This problem may not be improved even by further development of liquid crystal material with a shorter response time nor the orientation technology. An underlying cause of the problem is based on a fundamental principle of the active matrix type LCD, and reported in improving the Moving-Image Quality of TFT-LCDs at the International Display Research Conference (IDRC), 1997.
FIG. 9 is an schematic view illustrating the problem of moving image quality of a active matrix type LCD of the related art. Image data for each frame is shown at the left hand side of FIG. 9, and visual picture appear on a display screen (hereafter, called visual screen image) is shown at the right hand side of FIG. 9. An image data SIG1 at a frame 1 shows, for example, an alphabetical character of X. The next frame (frame 2) also shows the same character X except a slight shift toward right hand side. The bottom frame (frame 3) also shows the character X shifting toward a bottom-left direction. On the other hand, residual images (shadows) may be appeared in visual screen image, which actually recognized by human eyes, when the frame changes from the frame 1 to the frame 2 and the frame 2 to the frame 3. Because of these shadows, the problem of the active matrix type LCD of the related art on the capability of moving image generation with clear outlines is left unsolved.
FIG. 10 is a waveform diagram schematically showing a driving method of the active matrix type LCD of the related art shown in FIG. 9. In general, the LCD is driven in an AC mode. Accordingly, each frame (for example frame 1) is divided into a field 1 and a field 2, and the LCD is an interlace driven. In the frame 1, image data SIG1 is written into liquid crystal pixels for a period of the filed 1 and the field 2. In the next frame (frame 2), image data SIG2 is similarly written into the liquid crystal pixels for a period of the filed 1 and the field 2. The image data written into each liquid crystal pixel is kept during the frame pertain in the active matrix type driving method. When the frame is changed to the next frame, the image data is re-written instantaneously. Namely, the image data is suddenly switched between the frame 1 and the frame 2, whereby causing the residual image phenomenon. Human eyes recognize the residual image at switching of the frames in which, for example, the liquid crystal pixel write-in the white at the frame 1 is switched to the black at the frame 2.
Brightness of image shown on the CRT screen attenuates in an order of microsecond. In contrast, a fundamental principle of display method for the LCD is to keep the same display image for an entire frame. The LCD displays the same image until the switching of the frames starts. This will be added to the residual image phenomenon of human eyes described above. Accordingly, the residual image may be still recognized even after the frame has been changed despite of ultimate advancement in the response characteristics of the liquid crystal material. That is the fundamental problem on the moving image quality of the active matrix type LCD.
To solve the problem, utilization of xe2x80x9cOBC modexe2x80x9d technique is suggested by the report mentioned above to improve the moving image quality. The OBC mode technique is a technology for cutting the residual image recognized by the human eyes with assumption of the liquid crystal response time of about 5 msec. For example, in the transmission type LCD, a back light is blinked within single frame so as to display an image at the former part of the frame and tune the back light off at the latter part whereby inducing phenomenon similar to the fast attenuation of the CRT brightness. However, there are some drawback in the technique. For one thing, the contrast of the LCD is decreased since the blinking of the back light causes decrease of an average luminosity and darken the screen. Furthermore, a power consumption and production cost will increase due to the intermittent drive of the back light. Furthermore, the technique can not be applied to a reflection type LCD which is widely used in the present days. Some improvements are reported in AN ovel Wide-viewing-Angle Motion-Picture LCD Society of International Display, 1998 regarding problems on the back light power consumption and its application to the reflection type LCD. However, the report did not provide solutions of the problems on brightness and contrast of the LCD.
The present invention is carried out by taking into account the above mentioned problems relating to the conventional technology. An object of the present invention is to provide an active matrix type liquid crystal display apparatus capable of improving image quality of motion picture displayed thereon. The followings are provided to attain the object of the present invention. According to an embodiment of the present invention, there is provided a driving method of a liquid crystal display apparatus including a plurality of liquid crystal pixels disposed in an row-column matrix configuration, a line drive circuit sequentially scanning each line of the liquid crystal pixels at every frame repeating with a predetermined frequency, and a column drive circuit writing image signal into the liquid crystal pixels in sync with the sequential scanning, comprising the steps of dividing the every frame into a preceding sub-frame and a following sub-frame, performing the sequential scanning for the preceding sub-frame and performing the sequential scanning again for the following sub-frame, and writing an image signal originally assigned to a frame pertain into the liquid crystal pixels in sync with the sequential scanning for the preceding sub-frame and writing an image signal for adjusting image quality into the liquid crystal pixels in sync with the sequential scanning for the following sub-frame. The image signal for adjusting image quality is obtained by operating the image signal originally assigned to the frame pertain and an image signal assigned to a frame following the frame pertain. Alternatively, an image signal for adjusting image quality, which may be obtained by averaging the image signal originally assigned to a frame pertain and an image signal assigned to a frame following the frame pertain, is written into the liquid crystal pixels. Furthermore, the image signals may be written into liquid crystal pixels having a response characteristic of 10 msec or less.
Furthermore, according to an embodiment of the present invention, there is provided a driving method of a liquid crystal display apparatus including a plurality of liquid crystal pixels disposed in an row-column matrix configuration, a line drive circuit sequentially scanning each line of the liquid crystal pixels at every frame repeating with a predetermined frequency, and a column drive circuit writing image signal into the liquid crystal pixels in sync with the sequential scanning, comprising the steps of dividing the every frame into a preceding sub-frame and a following sub-frame, performing the sequential scanning for the preceding sub-frame and performing the sequential scanning again for said following sub-frame, and writing an image signal originally assigned to a frame pertain into the liquid crystal pixels in sync with the sequential scanning for the preceding sub-frame and writing an image signal for adjusting image quality into the liquid crystal pixels in sync with the sequential scanning for the following sub-frame. The image signal for adjusting image quality is obtained by performing an reduction operation on the image signal originally assigned to a frame pertain. Alternatively, an image signal for adjusting image quality, which may be obtained by reducing the image signal originally assigned to a frame pertain by half, may be written into the liquid crystal pixels. Furthermore, the image signals may be written into liquid crystal pixels having a response characteristic of 10 msec or less.
Furthermore, according to an embodiment of the present invention, there is provided a driving method of a liquid crystal display apparatus including a plurality of liquid crystal pixels disposed in an row-column matrix configuration, a line drive circuit sequentially scanning each line of the liquid crystal pixels at every frame repeating with a predetermined frequency, and a column drive circuit writing image signal into the liquid crystal pixels in sync with the sequential scanning, comprising the steps of dividing the every frame into a preceding sub-frame and a following sub-frame, performing the sequential scanning for the preceding sub-frame and performing the sequential scanning again for the following sub-frame, and writing an image signal originally assigned to a frame pertain into the liquid crystal pixels in sync with the sequential scanning for the preceding sub-frame and writing an image signal for adjusting image quality into the liquid crystal pixels in sync with the sequential scanning for the following sub-frame. The image signal for adjusting image quality is set to an image signal representative of a predetermined halftone level. Alternatively, the image signals may be written into liquid crystal pixels having a response characteristic of 10 msec or less.
According to an embodiment of the present invention, a frame is divided into a preceding sub-frame and a following sub-frame. In the preceding sub-frame, an image signal originally assigned to a frame pertain is written into the liquid crystal pixels. In the following sub-frame, an image signal for adjusting image quality, which is different from the image signal originally assigned to the frame pertain, is written into the liquid crystal pixels. The image signal for adjusting image quality is introduced so as to cut the residual image phenomenon occurred at an instant of switching a frame to the next frame.
According to an embodiment of the present invention, the image signal for adjusting image quality is obtained by using image data relating to a frame pertain and/or a frame next to the frame pertain. Accordingly, required brightness may be obtained since an image signal representative of black display is not used for the image signal for adjusting image quality during the following sub-frame.
Furthermore, according to an embodiment of the present invention, there is provided a driving method of a liquid crystal display apparatus including a plurality of liquid crystal pixels disposed in an row-column matrix configuration, a line drive circuit scanning lines of said liquid crystal pixels at every frame, and a column drive circuit writing image data into said liquid crystal pixels in sync with said line scanning, comprising the steps of dividing said every frame into a plurality of sub-frames, performing said line scanning for every sub-frame, and writing an image data originally assigned to a frame pertain into said liquid crystal pixels in sync with said line scanning for one of said sub-frames of said frame pertain, and writing an image data for adjusting image quality into said liquid crystal pixels in sync with said line scanning for a sub-frame other than said one of said sub-frames, said image data for adjusting image quality being obtained by operating at least using said image signal originally assigned to said frame pertain.